Method for electrical interconnection between printed wiring board layers using through holes with solid core conductive material

ABSTRACT

The present invention provides a printed wiring board and a method of manufacture therefor. The printed wiring board constructed according to the teachings of the present invention includes a printed wiring board dielectric layer having conductive foils located on at least two sides thereof. The printed wiring board further includes a solid core conductive material interconnecting the conductive foils.

TECHNICAL FIELD OF THE INVENTION

The present invention is directed, in general, to a printed wiring boardand, more specifically, to a printed wiring board including a solid coreconductive material and a method of manufacture therefor.

BACKGROUND OF THE INVENTION

Printed wiring boards (PWBs) are an integral part of electronicequipment and there have been continuing efforts to increase theinterconnection density and electrical efficiency of PWBs and thusdecrease their size and cost. The technology relating to PWBs goes backa number of years and, in general, a printed circuit is patterned on acopper foil which is located on the surface of a dielectric materialsuch as a plastic substrate. These boards vary in design and may have acopper foil on each surface of the plastic substrate, usually epoxy,(termed 2-sided boards)or they can be multi-layer boards which have aplurality of interleaved parallel planar copper foils and epoxy layers.In both types, through-holes are drilled in the board and metal platedto facilitate connection between the copper foil circuits.

Unfortunately, the copper plated through holes used in theseconventional structures are susceptible to barrel cracking duringqualification testing, e.g., thermal cycling. The barrel cracking, asthose skilled in the art are aware, negatively affects the electricalcharacteristics of the PWB. The industry has contemplated drilling asmall enough through hole in the PWB that the copper plating would filland thereby prevent the barrel cracking. Unfortunately, the throughholes have typically high aspect ratios, and the filling of the holeswith copper using the plating technique would undeniably block one endof the hole, thus trapping unwanted matter therein. Again, theelectrical characteristics of the PWB would be compromised.Additionally, during plating of the through holes copper is alsodeposited on the flat external surfaces of the PWB, resulting in thickercopper layers. These thicker copper layers tend to impede subtractivefine line patterning.

Accordingly, what is needed in the art is an electrical connectionbetween PWB layers that does not experience the problems or drawbacksexperienced or introduced by the prior art electrical connections.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, thepresent invention provides a printed wiring board and a method ofmanufacture therefor. The printed wiring board constructed according tothe teachings of the present invention includes a printed wiring boarddielectric layer having conductive foils located on at least two sidesthereof. The printed wiring board further includes a solid coreconductive material located in the printed wiring board dielectric layerand interconnecting the conductive foils.

As indicated above, the present invention further provides a method formanufacturing the aforementioned printed wiring board. Among otherelements, the method for manufacturing the printed wiring board includesproviding a printed wiring board dielectric layer having conductivefoils located on at least two sides thereof, and inserting a solid coreconductive material within the printed wiring board dielectric layer,thereby interconnecting the conductive foils.

Additionally, the present invention provides an electronic subassemblyincluding the aforementioned printed wiring board. The electronicsubassembly, among other elements, includes: 1) a printed wiring board,including a printed wiring board dielectric layer having conductivefoils located on at least two sides thereof and a solid core conductivematerial located in the printed wiring board dielectric layer andinterconnecting the conductive foils, and 2)electronic componentslocated on one or more surfaces of the printed wiring board.

The foregoing has outlined preferred and alternative features of thepresent invention so that those skilled in the art may better understandthe detailed description of the invention that follows. Additionalfeatures of the invention will be described hereinafter that form thesubject of the claims of the invention. Those skilled in the art shouldappreciate that they can readily use the disclosed conception andspecific embodiment as a basis for designing or modifying otherstructures for carrying out the same purposes of the present invention.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read with the accompanying FIGUREs. It is emphasized that, inaccordance with the standard practice in the industry, various featuresare not drawn to scale. In fact, the dimensions of the various featuresmay be arbitrarily increased or reduced for clarity of discussion.Reference is now made to the following descriptions taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 illustrates a cross-sectional view of one embodiment of a printedwiring board (PWB) constructed in accordance with the principles of thepresent invention;

FIG. 2 illustrates a cross-sectional view of an alternative embodimentof a PWB that has been constructed in accordance with the principles ofthe present invention;

FIG. 3 illustrates a cross-sectional view of a partially completed PWBat an initial stage of manufacture;

FIG. 4 illustrates a cross-sectional view of the partially completed PWBillustrated in FIG. 3 as an insertion means approaches the firstconductive foil;

FIG. 5 illustrates a cross-sectional view of the partially completed PWBillustrated in FIG. 4 as the insertion means penetrates the firstconductive foil, dielectric layer and second conductive foil;

FIG. 6 illustrates a cross-sectional view of the partially completed PWBillustrated in FIG. 5 as the insertion means is being removed from thesecond conductive foil, dielectric layer and first conductive foil;

FIG. 7 illustrates a cross-sectional view of the partially completed PWBillustrated in FIG. 6 as the insertion means is completely removed fromthe PWB and a cutting tool severs the solid core conductive material,thereby forming the solid core conductive material;

FIG. 8 illustrates a cross-sectional view of the partially completed PWBillustrated in FIG. 7 after additional solid core conductive materialportions are inserted in the dielectric layer;

FIG. 9 illustrates a cross-sectional view of the partially completed PWBillustrated in FIG. 8 after a scrubbing means removes excess solid coreconductive material extending from the first and second conductivefoils; and

FIG. 10 illustrates a cross-sectional view of an electronic subassemblyincorporating a PWB constructed according to the principles of thepresent invention.

DETAILED DESCRIPTION

Referring initially to FIG. 1, illustrated is a cross-sectional view ofone embodiment of a printed wiring board (PWB) 100 constructed inaccordance with the principles of the present invention. The PWB 100illustrated in FIG. 1 includes, as is standard, a printed wiring boarddielectric layer 110 having conductive foils 120, 125, located on atleast two sides thereof. In the particular embodiment shown in FIG. 1,the conductive foils 120, 125, happen to be located on opposing sides ofthe dielectric layer 110.

The dielectric layer 110 may comprise a multitude of different materialswhile staying within the scope of the present invention. Similarly, theconductive foils 120, 125, may include a number of different materials.For example, while the present invention will be discussed throughout ashaving copper conductive foils, those skilled in the art understand thatalmost any known or hereafter discovered conductive foil could be usedfor the conductive foils 120, 125.

Located within the dielectric layer 110 in the embodiment shown anddiscussed with respect to FIG. 1 is a solid core conductive material130. The solid core conductive material 130, or in this embodiment thethree solid core conductive materials 130, interconnect the conductivefoils 120, 125. Particularly, the solid core conductive material 130electrically connects the conductive foils 120, 125.

In the particular embodiment of FIG. 1, the solid core conductivematerial 130 comprises a solid core wire that has been inserted into thedielectric layer 110. For example, a solid core copper wire or anotherconductive wire could be used. As the solid core conductive material 130is solid, as compared to the conventional hollow plated through holes,the solid core conductive material 130 may have a smaller diameter thanthe conventional hollow plated through holes while providing the samecurrent carrying capacity. For example, in an exemplary embodiment thesolid core conductive material 130 may have a diameter that ranges fromabout 0.050 mm to about 0.200 mm, and preferably a diameter that rangesfrom about 0.100 mm to about 0.150 mm, while providing the desiredcurrent carrying capacity required for the PWB 100 to operate properly.In support of this, it is believed that a 0.150 mm diameter solid corecopper conductive material 130 has the equivalent current carryingcapacity as a 0.375 mm diameter by 0.015 mm thick copper plated throughhole.

Accordingly, the advantages of using the solid core conductive material130 rather than the prior art hollow plated through holes, are abundant.First, no metal plating of the through holes or epoxy filling of theplated through holes is required. Both these steps are costly and timeconsuming processes. Additionally, the solid core conductive material130 does not experience the barrel cracking issues experienced by theprior art plated through holes. Likewise, as no panel plating isrequired to plate the through holes, the conductive foil thickness maybe thinner. As those skilled in the art are aware, the thinnerconductive foils make finer pattern design rules possible.

In addition to those benefits disclosed in the paragraph above, betterpacking density can be achieved as the diameter of the solid coreconductive material 130 is smaller than the plated through holes for thesame current carrying values. Additionally, the solid core conductivematerial 130 provides improved thermal dissipation due to the solidmetal cross-section.

Turning briefly to FIG. 2, illustrated is a cross-sectional view of analternative embodiment of a PWB 200 that has been constructed inaccordance with the principles of the present invention. The PWB 200illustrated in FIG. 2 is similar to the PWB 100 illustrated in FIG. 1,with the exception that it includes additional dielectric substrates andconductive foils, thus, representing a multilayer PWB. For example, thePWB 200 of FIG. 2 includes a first dielectric layer 210 having first andsecond conductive foils 220, 225, located on opposing sides thereof. ThePWB 200 further includes a second dielectric layer 230 and a thirdconductive foil 240 contacting the first conductive foil 220, as well asa third dielectric layer 250 and fourth conductive foil 260 contactingthe second conductive foil 225. In the embodiment of FIG. 2, solid coreconductive material 270 interconnects the first, second, third andfourth conductive foils 220, 225, 240, 260, respectively.

Turning now briefly to each of FIGS. 3-9, illustrated arecross-sectional views of detailed manufacturing steps instructing howone might, in an advantageous embodiment, manufacture a PWB similar tothe PWB 100 depicted in FIG. 1. FIG. 3 illustrates a cross-sectionalview of a partially completed PWB 300 at an initial stage ofmanufacture. The PWB 300 illustrated in FIG. 3 includes a conventionalprinted wiring board dielectric layer 310 having first and secondconductive foils 320, 325, located on opposing sides thereof. Theconventional dielectric layer 310 may comprise many materials, however,an organic dielectric layer has been observed to work well. Likewise,the conventional dielectric layer 310 may have varying thicknesses,including conventional thicknesses ranging from about 0.060 mm to about0.800 mm.

Similarly, the first and second conductive foils 320, 325, may comprisemany materials. While copper may be the most common conductive foilused, those skilled in the art understand that other materials, such asaluminum, could just as easily be used. The first and second conductivefoils 320, 325, among others, may have thicknesses ranging from about0.005 mm to about 0.075 mm. As the process for forming the first andsecond conductive foils 320, 325, on the dielectric layer 310 isconventional, no details are required.

Turning now to FIG. 4, illustrated is a cross-sectional view of thepartially completed PWB 300 illustrated in FIG. 3 as an insertion means410 approaches the first conductive foil 320. The insertion means 410,which may be a sharp hollow object such as a needle, has a solid coreconductive material 420 located therein. At this point in themanufacturing process it may be advantageous to increase the temperatureof the PWB 300 to allow the insertion means 410 to penetrate therethrough easier. It is believed that a temperature ranging from about 50°C. to a temperature of less than about a glass transition temperature ofthe dielectric layer 310, is optimal. Other temperatures are, however,within the scope of the present invention.

As is illustrated in FIG. 4, a control means 430, such as a chuck, maybe used to control a feed of the solid core conductive material 420. Forexample, depending on the position of the solid core conductive material420, and the stage of manufacture of the partially completed PWB 300,the control means 430 may be in a closed position, in an open position,moving toward the tip of the insertion means 410, moving away from thetip of the insertion means 410, or any combination thereof. In theillustrative embodiment of FIG. 4, the control means 430 is holding thesolid core conductive material 420 in a fixed position relative to theinsertion means 410.

Turning now to FIG. 5, illustrated is a cross-sectional view of thepartially completed PWB 300 illustrated in FIG. 4 as the insertion means410 penetrates the first conductive foil 320, dielectric layer 310 andsecond conductive foil 325. The insertion means 410 should penetrate farenough into the second conductive foil 325 that the solid coreconductive material 420 is capable of electrically connecting the firstand second conductive foils 320, 325. As such, as shown in FIG. 5, it isoptimal to insert the insertion means 410 entirely through the secondconductive foil 325. In the embodiment shown in FIG. 5, the solid coreconductive material 420 extends a distance past the surface of thesecond conductive foil 325. As is illustrated in FIG. 5, the controlmeans 430 helps position the solid core conductive material 420 toextend past the surface of the second conductive foil 325.

Turning now to FIG. 6, illustrated is a cross-sectional view of thepartially completed PWB 300 illustrated in FIG. 5 as the insertion means410 is being removed from the second conductive foil 325, dielectriclayer 310 and first conductive foil 320. The insertion means 410 shouldbe removed in such a fashion as to cause the solid core conductivematerial 420 to remain within the second conductive foil 325, dielectriclayer 310 and first conductive foil 320. While this may be accomplishedin one of many ways, it is believed that as the insertion means 410 isretracted from the PWB 300, the solid core conductive material 420 isheld in place by the slightly shrinking hole formed by the insertionmeans 410.

Turning now to FIG. 7, illustrated is a cross-sectional view of thepartially completed PWB 300 illustrated in FIG. 6 as the insertion means410 is completely removed from the PWB 300 and a cutting tool 710 seversthe solid core conductive material 420, thereby forming the solid coreconductive material 720. The cutting tool 710, which may be any kind ofobject capable of separating the solid core conductive material 720 fromthe solid core conductive material 420, desirably leaves a small portionof the solid core conductive material 720 above the surface of the firstconductive foil 320. This small portion confirms that the solid coreconductive material 720 extends entirely through the second conductivefoil 325, dielectric layer 310 and first conductive foil 320, andestablishes that the second conductive foil 325 and first conductivefoil 320 are electrically interconnected with one another.

Turning now to FIG. 8, illustrated is a cross-sectional view of thepartially completed PWB 300 illustrated in FIG. 7 after additional solidcore conductive material portions 810, 820, are inserted in thedielectric layer 310. The additional solid core conductive materialportions 810, 820, have been formed in a similar manner as the solidcore conductive material 720.

Turning now to FIG. 9, illustrated is a cross-sectional view of thepartially completed PWB 300 illustrated in FIG. 8 after a scrubbingmeans 910 removes excess solid core conductive material extending fromthe first and second conductive foils 320, 325. The scrubbing means 910may be any known or hereafter discovered scrubbing means capable ofremoving the excess solid core conductive material. In addition toremoving the excess solid core conductive material, the scrubbing means910 advantageously smooths the surface of the first and secondconductive foils 320, 325. After removing the excess solid coreconductive material extending from the first and second conductive foils320, 325, the manufacturing process would continue by patterning certainportions of the first and second conductive foils 320, 325.

Turning briefly to FIG. 10, illustrated is a cross-sectional view of anelectronic subassembly 1000 incorporating a PWB constructed according tothe principles of the present invention. The electronic subassembly 1000includes a PWB 1010 somewhat similar to the PWB 100 shown and discussedwith respect to FIG. 1. For example, the PWB 1010 includes a dielectriclayer 1020 having first and second conductive foils 1030, 1035, locatedon opposing sides thereof. The PWB further includes three solid coreconductive material portions 1040 interconnecting the first and secondconductive foils 1030, 1035. The electronic subassembly 1000 furtherincludes electronic components 1050, 1060, located on one or moresurfaces of the PWB 1010. In the particular embodiment illustrated inFIG. 10, the electronic components 1050, 1060, are an integrated circuitand resistor, respectively, and are located on the first conductive foil1030. While the electronic components have been illustrated as anintegrated circuit and a resistor in the embodiment of FIG. 10, thoseskilled in the art understand that other types of electronic componentsare within the scope of the present invention. Additionally, while onlytwo electronic components are illustrated in the embodiment of FIG. 10more than two electronic components will generally be used on either orboth conductive foils 1030, 1035.

Although the present invention has been described in detail, thoseskilled in the art should understand that they can make various changes,substitutions and alterations herein without departing from the spiritand scope of the invention in its broadest form.

1. A printed wiring board, comprising: a printed wiring board dielectriclayer having a conductive foil located on at least two sides thereof;and a solid core conductive material located in said printed wire boarddielectric layer and interconnecting said conductive foils.
 2. Theprinted wiring board as recited in claim 1 wherein said solid coreconductive material is a solid core wire.
 3. The printed wiring board asrecited in claim 2 wherein said solid core wire is a solid core copperwire.
 4. The printed wiring board as recited in claim 1 wherein saidsolid core conductive material has a diameter ranging from about 0.050mm to about 0.200 mm.
 5. The printed wiring board as recited in claim 4wherein said solid core conductive material has a diameter ranging fromabout 0.100 mm to about 0.150 mm.
 6. The printed wiring board as recitedin claim 1 wherein said printed wiring board dielectric layer is a firstdielectric layer and first and second conductive foils are located onopposing sides thereof, and further including a second dielectric layerand third conductive foil contacting said first conductive foil and athird dielectric layer and a fourth conductive foil contacting saidsecond conductive foil, wherein said solid core conductive materialinterconnects said first, second, third and fourth conductive foils. 7.The printed wiring board as recited in claim 1 wherein said printedwiring board dielectric layer has a thickness ranging from about 0.060mm to about 0.800 mm and said conductive foils each have a thicknessranging from about 0.005 mm to about 0.075 mm.
 8. A method formanufacturing a printed wiring board, comprising: providing a printedwiring board dielectric layer having conductive foils located on atleast two sides thereof; inserting a solid core conductive materialwithin said printed wiring board dielectric layer, therebyinterconnecting said conductive foils.
 9. The method as recited in claim8 wherein inserting a solid core conductive material within said printedwiring board dielectric layer includes inserting a solid core wirewithin said printed wiring board dielectric layer.
 10. The method asrecited in claim 9 wherein inserting a solid core wire within saidprinted wiring board dielectric layer includes inserting a solid corecopper wire within said printed wiring board dielectric layer.
 11. Themethod as recited in claim 8 wherein said solid core conductive materialhas a diameter ranging from about 0.050 mm to about 0.200 mm.
 12. Themethod as recited in claim 11 wherein said solid core conductivematerial has a diameter ranging from about 0.100 mm to about 0.150 mm.13. The method as recited in claim 8 wherein inserting a solid coreconductive material within said printed wiring board dielectric layerincludes inserting a solid core conductive material within said printedwiring board dielectric layer using a sharp hollow object.
 14. Themethod as recited in claim 13 wherein inserting a solid core conductivematerial within said printed wiring board dielectric layer using a sharphollow object includes inserting a solid core conductive material withinsaid printed wiring board dielectric layer using a needle.
 15. Themethod as recited in claim 8 further including increasing a temperatureof said printed wiring board dielectric substrate prior to insertingsaid solid core conductive material within said printed wiring boarddielectric layer.
 16. The method as recited in claim 15 wherein saidtemperature ranges from about 50° C. to a temperature less than a glasstransition temperature of said printed wiring board dielectric layer.17. The method as recited in claim 8 wherein said printed wiring boarddielectric layer is a first dielectric layer and first and secondconductive foils are located on opposing sides thereof, and furtherincluding forming a second dielectric layer and third conductive foilcontacting said first conductive foil and a third dielectric layer and afourth conductive foil contacting said second conductive foil, whereinsaid solid core conductive material interconnects said first, second,third and fourth conductive foils.
 18. An electronic subassembly,comprising: a printed wiring board, including; a printed wiring boarddielectric layer having conductive foils located on at least two sidesthereof; and a solid core conductive material located in said printedwiring board dielectric layer and interconnecting said conductive foils;and electronic components located on one or more surfaces of saidprinted wiring board.
 19. The electronic subassembly as recited in claim18 wherein said solid core conductive material is a solid core wire. 20.The electronic subassembly as recited in claim 18 wherein said solidcore conductive material has a diameter ranging from about 0.050 mm toabout 0.200 mm.